Theoretical and experimental studies were undertaken to explain the mechanisms that establish conditions for the occurrence of the one-dimensional deflagration-to-detonation transition (DDT), and to formulate a satisfactory model for a quantitative description of this transition. The theoretical studies were concerned with the thermo-hydrodynamic treatment of DDT. The central problem is to model the propagation of the unsteady flame and the flow it produces ahead of the flame front. The compressive flows produced by an accelerating flame and by an accelerating piston were compared to provide a better physical understanding of the compressive action of an accelerating flame; conditions for shock formation in a compressive flow were formulated. The condition for shock formation in the compressed state is that the second derivative of the Lagrange pressure-specific volume compression curve be positive. When this condition is satisfied, a shock is always formed by an accelerating piston but not always by an accelerating flame. As the piston accelerates, the compression waves emanating from it overtake each other and coalesce to form a shock. But the accelerating flame can overtake and consume compressed material before the compression waves emanating from it coalesce to form a shock. In the experimental study, an assembly was designed to allow incorporation of stress gages into propellant charges during the casting process, thereby eliminating the expensive machining and grooving operations conventionally used in constructing targets for langrange gage experiments.